Vehicle engines generally comprise accessories that are used in the operation of the engine and vehicle. Such accessories can include a power steering pump, an air conditioning compressor, an alternator, an oil pump, a fuel pump and so on. These accessories are generally driven by a serpentine belt. The serpentine belt engages a pulley on each accessory as well as on an engine crankshaft. The engine crankshaft provides the torque to drive the accessories.
As the belt is driven by the crankshaft it is necessarily subject to engine speed variations during acceleration and deceleration of the vehicle. In other words the operating speed of the accessories is directly proportional to the speed of the engine.
The variations in engine speed, particularly engine speeds greater than idle, result in inefficient operation of the accessories because each accessory must be designed to operate satisfactorily over the entire engine speed range. This necessarily means that the efficiency is less than optimum for most of the engine speed range. Further, at higher engine speeds greater power is required to drive the accessories, resulting in reduced fuel efficiency and reduced available torque. Therefore it is desirable to decouple some or all of the accessories from the engine crankshaft so they can be driven at a lower and narrower optimum speed range.
Representative of the art is U.S. Pat. No. 5,700,121 (1997) to Meckstroth which discloses a system for powering various rotating vehicle accessories.
The prior art requires the accessories to be disengaged from the engine at engine start for the purpose of “helping” a minimally sized starter. Further, the prior art does not teach a clutch unit combined with a crankshaft damper for reducing application of engine vibration.
What is needed is a dual ratio belt drive system having a clutch unit with an electromagnetic clutch that is engaged at engine start. What is needed is a dual ratio belt drive system further comprising a clutch unit having a crankshaft damper. The present invention meets these needs.